This invention relates to improvements in current measurement circuits and to methods of testing the integrity of such circuits.
It is well known that the current flowing along a path in an electrical circuit can be measured by measuring the potential drop across a resistor connected in series within the path. Through the application of Ohm's Law the current is given as I=(Vi−Vo)/R where Vi and Vo are the input and output voltages to the resistor in Volts and R is the resistance in Ohms.
The measurement of potential drop is typically made by connecting the input and output side of the resistor to the positive and negative input terminals of a differential amplifier and then to a microprocessor which converts the output of the differential amplifier into a current value if required. It is also common to provide some filtering between the voltage take offs from the resistor and the inputs to the amplifier, both to remove any high frequency noise and to aid high frequency common mode rejection of the amplifier. In its simplest form this may comprise a first order low pass filter comprising a single resistor and capacitor. Even with such a low number of components failures can occur which will cause erroneous current measurements to be made.